Network Layer: Address Mapping, Error Reporting, and Multicasting Study Notes

  • Delivery of a packet to a host or router requires two levels of addresses: logical and physical. A physical address identifies a host or router at the physical level.
  • Mapping of a logical address to a physical address can be static or dynamic.
  • Static mapping involves a list of logical and physical address correspondences; maintenance of the list requires high overhead.
  • The address resolution protocol (ARP) is a dynamic mapping method that finds a physical address, given a logical address.
  • In proxy ARP, a router represents a set of hosts. When an ARP request seeks the physical address of any host in this set, the router sends its own physical address. This creates a subnetting effect.
  • Reverse Address Resolution Protocol (RARP) is a form of dynamic mapping in which a given physical address is associated with a logical address.
  • ICMP sends four pairs of query messages: echo-request and echo-reply, time-stamp request and reply, address-mask-request and -reply, and router solicitation and advertisement.
  • The checksum for ICMP is calculated by using both the header and the data fields of the ICMP message.
  • Packet InterNet Groper (ping) is an application program that uses the services of ICMP to test the reachability of a host.
  • Multicasting is the sending of the same message to more than one receiver simultaneously.
  • The Internet Group Management Protocol (IGMP) helps multicast routers create and update a list of loyal members related to a router interface.
  • The three IGMP message types are the query message, the membership report, and the leave report.
  • A delayed response strategy prevents unnecessary traffic on a LAN.
  • The IGMP message is encapsulated in an IP datagram.
  • Most LANs, including Ethernet, support physical multicast addressing.
  • WANs that do not support physical multicast addressing can use a process called tunneling to send multicast packets.
  • BOOTP and Dynamic Host Configuration Protocol (DHCP) are client/server applications that deliver vital network information to either diskless computers or computers at first boot.
  • A BOOTP request is encapsulated in a UDP user datagram.
  • BOOTP, a static configuration protocol, uses a table that maps IP addresses to physical addresses.
  • A relay agent is a router that helps send local BOOTP requests to remote servers.
  • DHCP is a dynamic configuration protocol with two databases: One is similar to BOOTP, and the other is a pool of IP addresses available for temporary assignment.
  • The DHCP server issues a lease for an IP address to a client for a specific time.
  • ICMPv6, like version 4, reports errors, handles group memberships, updates specific router and host tables, and checks the viability of a host.



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